only way for the life current to pass to the physical body is through the medium of the astral body. The physical body is dissolved when separated from the astral body because the impulse that animated it is removed. As the karana sharira is on the plane of devachan, the only place to which it can go on separation from the physical body is devachan, or swargam; but in separating itself from the astral body it takes with it all those impulses that were accumulated by the karma of the man during his successive incarnations.
These impulses subsist in it, and perhaps it does enjoy a new life in devachan--a life unlike any with which we are acquainted, but a life quite as natural to the entity that enjoys it as our conscious existence seems to be to us now. These impulses give rise to a further incarnation, because there is a certain amount of energy locked up in them, which must find its manifestation on the physical plane. It is thus karma that leads it on from incarnation to incarnation.
The natural region of the astral body is the bhuvarloka or the astral plane. To the astral plane it goes, and there it is detained. It very rarely descends into the physical plane, for the simple reason that the physical plane has no natural attraction for it. Moreover it necessarily follows that, just as the karana sharira cannot remain on the physical plane, the astral body cannot remain there either. This astral body loses its life